The invention relates to a device for reducing hydraulic-fluid oscillation in a hydraulic system, in particular in a hydraulic system of an aircraft, according to the precharacterising part of claim 1.
Hydraulic systems are used in a wide range of applications for conveying fluids that are used for a host of different purposes and may be conveyed at greatly different pressures. The fluids conveyed at pressure may perform mechanical work for control purposes or motive power purposes; they may be used as fuels or oxidising agents; they may be lubricants or other materials, any fluids, as used in motive power engineering, materials processing etc.
In aircraft, typically, several hydraulic systems that are usually independent are provided, which hydraulic systems by pumps, in particular axial piston pumps, generate the necessary pressure in the systems. In this arrangement pressure pulsation in the hydraulic lines occurs, which pulsation is acoustically perceived as disagreeable noise, and, because such pulsation subjects the lines to additional loads, it may also increase the possibility of leakages occurring. The undesirable side effects associated with such pressure pulsation occur in particular also in the case of pumps of aircraft engines.
According to the state of the art, pressure pulsation of the type mentioned may be reduced by reverberation attenuators, which however on the one hand have to be installed in close proximity to the pumps, and on the other hand, in particular in the case of engine pumps that operate at relatively low frequencies, have to be quite voluminous, which means that because of the lack of space they cannot be accommodated in the engine pylon in close proximity to the pumps.
From DE 103 16 946 A1 a device for attenuating pressure oscillation in a hydraulic line is known, in which device an actuator for generating pressure oscillation in the hydraulic line is arranged between a pressure source in the form of a pump and a consumer. By a control-/regulating device the actuator is to be controlled such that it generates pressure oscillation that is at least approximately in phase opposition to the pressure oscillation detected by a sensor in the hydraulic line. In this known device the actuator that generates the pressure oscillation that is in phase opposition is arranged in the hydraulic line at a smaller distance from the pump, i.e. upstream of the sensor that generates the pressure oscillation.
Furthermore, from the publication “The Vibration Active Control on the Fluid Borne Noise”, Jiao Zongxia, Chen Ping, Hua Quing, Wang Shaoping, College of Automation Science and Electrical Engineering, Beijing University of Aeronautics and Astronautics, a device for actively reducing hydraulic fluid oscillation in a hydraulic system is known. This hydraulic system comprises a pump that is provided for conveying the hydraulic fluid in a connected hydraulic fluid line system, and further comprises a first relief valve that is connected to the hydraulic line system. A second relief valve that is furthermore connected to the hydraulic line system is a piezoelectrically operable actively controllable valve that is provided for reducing the hydraulic-fluid oscillation in the hydraulic system. Said valve is actuated by fast Fourier transforms (FFT) carried out in a computer in response to the pressure oscillation registered on the hydraulic system. The hydraulic fluid that is led away by way of the actively controllable valve is collected as a leakage quantity and is returned to the hydraulic system. In addition to the useable feed quantity, the feed pump of this known hydraulic system thus also has to convey the quantity of hydraulic fluid that has been led away by way of the actively controllable valve and that has been collected as a leakage quantity.
Finally, from the Japanese patent abstract 05180390 a device for attenuating noise-generating oscillation in a line is known, in which device a first oscillation sensor is provided near a pump that is considered to be the primary oscillation source, which oscillation sensor is installed on the outside of the line and contains an oscillation acceleration detector, and, at a predetermined distance from said first oscillation sensor, an electromagnetic excitation device that is referred to as the secondary oscillation source is provided on the line. Again at a predetermined space from the electromagnetic excitation device, a second oscillation sensor, which also comprises an oscillation acceleration detector, is provided as a fault sensor. The first oscillation sensor, the fault sensor, and the electromagnetic excitation device are electrically connected to a filter circuit that serves as a regulating device so as to reduce the noise in the line, which noise has been generated by the oscillation.